1. Field of the Invention
The present invention relates to the field of recovery of scrap metals, and more particularly to the recovery and remelting of magnesium and magnesium alloy fines, chips and scraps.
2. Prior Art
Magnesium has been used in very substantial quantities for many years, both in the nearly pure form and in high magnesium content alloys. Though magnesium and high magnesium content alloys (hereinafter simply magnesium) present a very substantial fire hazard, machine shop and other processing operations for controlling the likelihood of occurrence of fires are well known, and consequently magnesium castings, machined parts and parts formed of other processes are commonly used in applications requiring the special properties of low density and a high strength to weight ratio. However, in spite of the routine use of magnesium for many years, no really satisfactory method of disposing of magnesium fines, chips and scraps has been found prior to the present invention. Accordingly machine shops and other operations processing magnesium have the constant problem of disposing of the waste magnesium, and have no practical way of recovering the magnesium for reuse.
One method which has been proposed in that of U.S. Pat. No. 3,634,066. In this method scrap metal particles and placed in an enclosed receptacle mounted above a molten metal bath. The receptacle is emerged in the molten bath such that either the base wall or a removable cover of the receptacle is submerged below the surface of the bath. The molten metal reacts with the atmosphere in the receptacle to create a partial vacuum, drawing molten metal into the receptacle to melt the scrap particles therein. The receptacle is then raised above the level of the metal bath to allow the melt to drain through the openings in the receptacle. This method overcomes the problem of attempting to maintain a flux or suitable gaseous environment around the bulky and very low effective density scrap metal during melting by confining the scrap in an oxidizing environment of limited capacity. However, it has various disadvantages which make its use difficult, particularly when the scrap must be transported for remelting. In particular, the disclosed method is directed only toward the remelting problem and does not include any method for storage or transportation in a manner to minimize the extent of oxidation which may occur by reaction with the environment and to minimize the possibility of fire. Also, the disclosed method purposely causes a reaction between a limited environment and the metal. Though volume of such reacting atmosphere is not large, the aggregate density of the metal chips typically is very low, so that a significant percentage material is lost through oxidation. Of course, the scrap must be substantially free of volatile contaminants such as moisture, cutting oils, etc., as a positive pressure in the receptacle creates problems not only in the receptacle, but with respect to the flux layer or controlled environment over the molten metal in the pot itself. The disclosed method has the further diadvantage of effectively increasing the effective crucible area exposed to the molten metal, thereby increasing the rate of contamination of the molten metal from this source.